The Castaway is asked to find Dorgan and let him know that Brogar wants to speak with him. After inquiring from Luis, the Hero is led to an old mine (called a "cave" by characters in the game) at the southeast end of the swamp. Here Dorgan's corpse is found, with many grave moths fluttering around in the same cavern. On his body can be found a piece of the sword from the Golden Fragments quest.
Although already dead at the start of the game, Dorgan is part of a much bigger plot. Brogar has been fleecing workers and hunters in the Don's camp, and Dorgan was the collector of these funds. This is one piece of evidence eventually used to prove to the Don that Brogar is trying to take over the camp.
He is dead at the start of the game. There is no way to save him or to have any kind of dialog with him.